Environmental and biological factors influencing Culex pipiens quinquefasciatus Say (Diptera: Culicidae) vector competence for Saint Louis encephalitis virus

Abstract

Complex interactions between environmental and biological factors influence the susceptibility of Culex pipiens quinquefasciatus to St. Louis encephalitis virus and could affect the epidemiology of virus transmission. Similar interactions could have epidemiologic implications for other vector-virus systems. We conducted an experiment to examine four such factors in combination: mosquito age, extrinsic incubation temperature (EIT), virus dose, and colony. The proportion of mosquitoes with body infections or disseminated infections varied between colonies, and was dependant on age, EIT, and dose. We also show that the probability of a body or leg infection interacted in complex ways between colonies, ages, EITs, and doses. The complex interactive effects of environmental and biological factors must be taken into account for studies of vector competence and epidemiology, especially when laboratory studies are used to generalize to natural transmission dynamics where the extent of variation is largely unknown.

Figure 1

Logit estimates from generalized linear mixed model showing the relationship between the occurrence of body or leg infection between different ages of mosquitoes (age × body part; F = 5.36, degrees of freedom = 2, 3367, P = 0.005). The estimated mean probability of infection (model-based estimate, see text for details) and the mean probability of infection (calculated from the data for the appropriate treatment groups combined) are plotted for different body parts (circle = body; triangle = leg). The probability of body infection differs between ages, but leg infections are more consistent between ages.

Figure 2

Logit estimates from generalized linear mixed model showing the relationship between the occurrence of body and leg infection between different ages, doses, and colonies (age × dose × colony; F = 3.83, degrees of freedom = 2, 3367, P = 0.022). The probability of infection and the estimated mean probability of infection are plotted for different colonies (circle = 1995 colony; triangle = 2007 colony). Colonies show different infection responses caused by age and dose. Means and estimated means are as in Figure 1.